Comparison of neutron noise solvers based on numerical benchmarks in a 2-D simplified UOX fuel assembly

In the CORTEX project, several solvers are developed and applied to analyze neutron noise problems. They are based on Monte Carlo and deterministic (higher-order transport and diffusion) methods. For the study of their validity and limitations, an extensive verification and validation work has been undertaken and includes the simulation of numerical exercises and experiments. In the current paper the solvers are compared over two neutron noise benchmarks defined in a 2-D simplified UOX fuel assembly, with Monte Carlo used as a reference. In the two exercises, a global neutron noise source and a combination of stationary perturbations of the various cross sections are respectively prescribed. The higher-order neutron transport methods provide consistent results with respect to Monte Carlo. The calculations obtained from the diffusion-based solvers show discrepancies that can be significant, in particular for the thermal amplitude of the neutron noise in the region close to the neutron noise source. All the solvers predict very similar values for the noise phase